Which event is endothermic? a)the burning of a matchb)the change of water vapor to a liquidc)the combustion of propane gasd)the melting of ice

Option (d) is the correct answer.

Explanation:

When heat is absorbed by reactant molecules then the reaction is known as endothermic reaction. In this reaction energy of products is more than the energy of reactant molecules.

For example, when ice is kept at room temperature then it absorbs heat from the surrounding and it start to melt. Therefore, solid state of water (ice) changes into liquid state of water.

Whereas when heat released by reactant molecules then the reaction is known as exothermic reaction. In this reaction energy of products is less that the energy of reactants.

For example, burning of a match is an exothermic reaction.

Thus, we can conclude that out of the given options event of melting of ice is endothermic.

the dissociation of nickel hydroxide is follows:

the concentration of hydroxide ion is

the equilibrium constant value of nickel hydroxide is = 6.1 * 10^-^1^6 and thus equilibrium equation can be written as:

thus, concentration of ni is 0.23 * 10^-^4 mol /l

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.